I am looking for an ebook reader which can highlight text in various colors. Everything should get synced across iOS and desktop. By sync, I mean that highlights I make in a PDF on one device should be treated as an editable highlight on the other device, and not as a permanent part of the PDF. This is to be used for textbooks. Currenty, I use Apple Books but it is very slow and I cannot sync it outside the Apple environment. I am okay with free options, self hosted options and one time purchases. I am not so keen on subscriptions but will consider a cheap one. Any help or advice is greatly appreciated.